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In this article, I consider the significance of the discovery of spermatozoa for Leibniz's deeply held beliefs that (i) no true substance can ever be generated or destroyed, except miraculously; and (ii) that every substance must be perpetually organically embodied. I further consider the way these beliefs are transformed as Leibniz's basic middle-period commitment to corporeal substance gives way (though not entirely) to a metaphysics of monadological immaterialsm. What endures throughout, I show, is the conviction that whatever is real must be indestructible, whether this is conceived as a form-matter compound in which the two components can never be entirely sundered from one another, or as a node of perception “absolutely destitute of parts”. Whatever the deepest metaphysical account of corporeality, Leibniz never abandons his interest in spermatozoa as the corporeal hosts of preexisting animals.

Leibniz's mill argument in 'Monadology' 17 is a well-known but puzzling argument against materialism about the mind. I approach the mill argument by considering other places where Leibniz gave similar arguments, using the same example of the machinery of a mill and reaching the same anti-materialist conclusion. In a 1702 letter to Bayle, Leibniz gave a mill argument that moves from his definition of perception (as the expression of a multitude by a simple) to the anti-materialist conclusion. Soon afterwards, in the Preface to the New Essays, Leibniz gave a different mill argument. That argument depends upon there being no arbitrary and inexplicable connections in nature, because God would not create such things. Later, in the 'Monadology', Leibniz again used the mill example in arguing against materialism. That passage too, I argue, uses an argument from inexplicability rather than from Leibniz's definition of perception.

I consider Leibniz's thoughts about Hobbes's materialism, focusing on his less-discussed later thoughts about the topic. Leibniz understood Hobbes to have argued for his materialism from his imagistic theory of ideas. Leibniz offered several criticisms of this argument and the resulting materialism itself. Several of these criticisms occur in texts in which Leibniz was engaging with the generation of British philosophers after Hobbes. Of particular interest is Leibniz's correspondence with Damaris Masham. Leibniz may have been trying to communicate with Locke, but ended up discussing Masham's version of the argument for materialism that Leibniz attributed to Hobbes.

Toward the end of 1676 Leibniz met Spinoza a number of times. In one of those meetings Leibniz presented a proof of the possibility of God's existence. In his proof Leibniz presupposed that a proposition is necessarily true only if its truth is either demonstrable or self-evident and that the divine perfections are simple and affirmative qualities. I contend that Leibniz's presuppositions undermine, rather than establish, the necessary existence of 'a God of the kind in whom the pious believe'. My assessment is based upon a consideration of Leibniz's argument in the context of other early papers, works written before the "Discourse on Metaphysics" in 1686.

Leibniz's predicate-in-notion principle and some of its alleged consequences, by C. D. Broad.--On Leibniz's metaphysics, by L. Couturat.--Philosophical reflections of Leibniz on law, politics, and the state, by C. J. Friedrich.--The root of contingency, by E. M. Curley.--Monadology, by M. Furth.--Individual substance, by I. Hacking.--Leibniz on plenitude, relations, and the "reign of the law," by J. Hintikka.--Leibniz's theory of the ideality of relations, by H. Ishiguro.--Leibniz and Spinoza on activity, by M. Kneale.--Leibniz and Newton, by A. Koyré.--Plenitude and sufficient reason in Leibniz and Spinoza, by A. O. Lovejoy.--Leibniz on possible worlds, by B. Mates.--Recent work on the philosophy of Leibniz, by B. Russell.--On Leibniz's explication of "necessary truth," by M. D. Wilson.--Bibliography (p. [421]-425).

Broad, C. D. Leibniz's predicate-in-notion principle and some of its alleged consequences.--Couturat, L. On Leibniz's metaphysics.--Friedrich, C. J. Philosophical reflections of Leibniz on law, politics, and the state.--Curley, E. M. The root of contingency. Furth, M. Monadology.--Hacking, I. Individual substance.--Hintikka, J. Leibniz on plenitude, relations, and the "reign of law."--Ishiguro, H. Leibniz's theory of the ideality of relations.--Kneale, M. Leibniz and Spinoza on activity.--Koyré, A. Leibniz and Newton.--Lovejoy, A. O. Plenitude and sufficient reason in Leibniz and Spinoza.--Mates, B. Leibniz on possible worlds.--Russell, B. Recent work on the philosophy of Leibniz.--Wilson, M. D. On Leibniz's explication of "necessary truth.".

When Heidegger pursues his destructive interpretation of Leibniz's doctrine of judgment, he identifies a principle of abyssal ground and a concealed metaphysics of truth that undermine the priority of logic with respect to ontology. His reading turns on an account of Leibniz's methodological generation of metaphysical principles and the relation between reason and identity, which, I argue, is at once deeply flawed and extremely productive. This essay pursues the implications of Heidegger's quickly abandoned suggestion that Leibniz's principle of identity is reflexively self-grounding, arguing that this claim makes possible a rigorous interpretation of Leibnizian method as an abyssal logic of repetition. I hold that the identification of such a methodology requires a modified account of the metaphysics of truth operative in Leibniz that reinvigorates Heidegger's reading even while moving beyond his now exhausted trope of a hidden presupposition of subjectivity.

Kant’s avowed commitment to the basic principles of Leibniz’s metaphysics is evident throughout the critical project and stated explicitly in the Prize Essay. However, it is not until the Critique of Judgment, wherein Kant recognizes that Judgment operating in its reflective mood can engender synthetic a priori claims, that Kant is fully capable of appropriating the basic tenets of Leibniz’s metaphysics. This paper examines Kant’s treatment of Leibniz from the perspective of the Critique of Judgment. It is argued that from this vantage point the metaphysics of Leibniz is viewed as fundamental for Kant’s critical project. Moreover, it is argued that it is not until the retrieval of Leibniz’s metaphysics that Kant has a basis for seeking the unity of pure and practical reason.

Leibniz viewed the principle of continuity, the principle that all natural changes are produced by degrees, as a useful heuristic for evaluating the truth of a theory. Since the Cartesian laws of motion entailed discontinuities in the natural order, Leibniz could safely reject it as a false theory. The principle of continuity has similar implications for analyses of Leibniz's theory of consciousness. I briefly survey the three main interpretations of Leibniz's theory of consciousness and argue that the standard account entails a discontinuity that Leibniz could not allow. I argue that the principle of continuity and the textual data favor an interpretation according to which a conscious mental state just is a perception that is distinct to a sufficient degree.

That Leibniz finds the philosophy of Spinoza horrifyingly wrong is obvious to anyone who reads Leibniz’s work; that Leibniz finds Spinozism so seductive that his own system is in danger of collapsing into it is less obvious but, I believe, equally true. The difference here is not so much between an exoteric and an esoteric philosophy suggested by Russell2 but between a thorough-going rationalism on the part of Spinoza and Leibniz’s “mitigated rationalism” – mitigated by the exigencies of his orthodox Christianity. In other words, it is Leibniz’s traditional view of the nature of God and his creatures that leads him to abhor Spinoza’s vision, while his own commitment to a number of principles and ideas pushes him to rationalism. And if Kant is right that the mind naturally desires a system, then Leibniz ought to see the Spinozistic consequences of many of his philosophical principles. Of course, there is nothing new in saying that the God of Spinoza and the God of Leibniz are fundamentally different, but I believe that if we focus on Leibniz’s critique of Spinoza’s account of the nature of God and a constellation of related concepts, we can come to a deeper understanding of the thought of both philosophers.